A personality thief is a person with a sever lack of knowledge in the how to of being a normal, funtioning social human being. He finds himself leaching off the personality of someone who is socially succesfully at the moment, and adopts their behavior in an attempt to fit in. However, this normally causes a backfire because of the obvious overkill present, and the pitifulness of the unoriginality.
Lashmeeeee: Wow, this is fucking clutch!
Lashmeeeee: "Failed attempt at an inside joke he's not apart of"
Victim: Lashmeeee you faggot, stop stealing my personality and get back in your fucking single!
Lugo: You fucking personality thief!
Fogey/fogy /fougi/ sl. (early 18C+, orig. Scot) old-fashioned, stuck-in-the mud.
Person with old fashioned ideas which he is unwilling to change: Come to the disco and stop being such an old fogey!
You think me an old fogeyand an old tory, his thoughtful voice said. I saw three generations since O’Connel’s time. I remember the famine. Do you know that the orange lodges agitated for repeal of the union twenty years before O’Connel did or before the prelates of your communion denounced him as a demagogue? You fenians forget some things. (James Joyce, Ulysses. PenguinBooks,1992. p. 38)